High-strength sputtering target for forming protective film for optical recording medium

ABSTRACT

A high-strength sputtering target for forming a protective film for an optical recording medium, obtained by sintering a mixed powder containing, in mol %, 10 to 70% of a zirconium oxide or hafnium oxide and 50% or less (over 0%) of silicon dioxide, and 0.1 to 8.4% of yttrium oxide as necessary, and the remainder containing aluminum oxide, lanthanum oxide, or indium oxide and inevitable impurities, wherein a complex oxide phase of Al 6 Si 2 O 13 , La 2 SiO 5 , or In 2 Si 2 O 7  is formed in a base of the target.

CROSS-REFERENCE TO PRIOR APPLICATION

This is the U.S. National Phase Application under 35 U.S.C. §371 ofInternational Patent Application No. PCT/JP2007/061643 filed Jun. 8,2007, which claims the benefit of Japanese Patent Application No.2006-159303 filed Jun. 8, 2006, both of which are incorporated byreference herein. The International Application was published inJapanese on Dec. 13, 2007 as WO2007/142333 A1 under PCT Article 21(2).

FIELD OF THE INVENTION

The present invention relates to a high-strength sputtering target(hereinafter, referred to as “target”) for forming a protective film foran optical recording medium which is capable of recording, reading out,repeatedly recording and reading out, and erasing information using alaser beam.

BACKGROUND OF THE INVENTION

It is generally known that protective films (hereinafter including bothlower and upper protective films) for an optical recording medium suchas a laser disk or the like typically include 20% of silicon dioxide(SiO₂) with the remaining part being zinc sulfide (ZnS). This protectivefilm is known to be obtained by carrying out sputtering with the use ofa target for forming a protective film for an optical recording medium,i.e., a ZnS—SiO₂ based hot-press sinter which includes 20% silicondioxide (SiO₂) with the remaining part being zinc oxide sulfide (ZnS).

However, such a protective film prepared by using a target composed of aZnS—SiO₂ based hot-press sinter causes a problem in that repeatablere-recording performance deteriorates when a laser beam is irradiated toa recording layer to repetitively perform re-recording since S in ZnS ofa target composed of a ZnS—SiO₂ based hot-press sinter diffuses in therecording layer. Consequently, development of a protective filmcontaining no S has been carried out. Examples of a protective filmcontaining no S, as follows, are known where values are in mol %.

(i) A protective film for an optical recording medium produced bysintering a mixed powder including 10 to 70% of zirconium oxide, and 50%or less (over 0%) of silicon dioxide, and the remainder containingaluminum oxide and inevitable impurities.

(ii) A protective film for an optical recording medium produced bysintering a mixed powder including 10 to 70% of hafnium oxide, 50% orless (over 0%) of silicon dioxide and the remainder containing aluminumoxide and inevitable impurities.

(iii) A protective film for an optical recording medium produced bysintering a mixed powder including 10 to 70% of zirconium oxide, 0.1 to8.4% of yttrium oxide, and 50% or less (over 0%) of silicon dioxide, andthe remainder containing aluminum oxide and inevitable impurities.

(iv) A protective film for an optical recording medium produced bysintering a mixed powder including 10 to 70% of zirconium oxide, and 50%or less (over 0%) of silicon dioxide, and the remainder containinglanthanum oxide and inevitable impurities.

(v) A protective film for an optical recording medium produced bysintering a mixed powder including 10 to 70% of hafnium oxide, and 50%or less (over 0%) of silicon dioxide, and the remainder containinglanthanum oxide and inevitable impurities.

(vi) A protective film for an optical recording medium produced bysintering a mixed powder including 10 to 70% of zirconium oxide, 0.1 to8.4% of yttrium oxide, and 50% or less (over 0%) of silicon dioxide, andthe remainder containing lanthanum oxide and inevitable impurities.

(vii) A protective film for an optical recording medium produced bysintering a mixed powder including 10 to 70% of zirconium oxide, and 50%or less (over 0%) of silicon dioxide, and the remainder containingindium oxide and inevitable impurities.

(viii) A protective film for an optical recording medium produced bysintering a mixed powder including 10 to 70% of hafnium oxide, and 50%or less (over 0%) of silicon dioxide, and the remainder containingindium oxide and inevitable impurities.

(ix) A protective film for an optical recording medium produced bysintering a mixed powder including 10 to 70% of zirconium oxide, 0.1 to8.4% of yttrium oxide, and 50% or less (over 0%) of silicon dioxide, andthe remainder containing indium oxide and inevitable impurities.

In addition, a target for forming protective films for an opticalrecording medium which have compositions described in the foregoing (i)to (ix) has been developed. This target has the same composition as theprotective films for an optical recording medium mentioned in (i) to(ix) above (refer to Japanese Patent Application Laid-Open No.2005-56545).

The target employs the oxide powders mentioned in the foregoing (i) to(ix) as a raw powder. The raw powders are mixed at a predetermined ratioand combined to prepare a mixed powder. The mixed powders are molded andbaked in air or an oxidative atmosphere such as an oxygen atmosphere,thereby producing the targets.

SUMMARY OF THE INVENTION

In targets produced by mixing oxide powders prepared as in (i) to (ix)as raw powders at a predetermined ratio and combining into mixedpowders, followed by molding and baking the mixed powders in anoxidative atmosphere under normal conditions, cracks occur duringhigh-power sputtering, and thus formation of a protective group for anoptical recording medium cannot be efficiently achieved.

An object of the present invention is to provide a high-strength targetfor forming a protective film for an optical recording medium in whichcracks do not occur even in high-power sputtering.

The inventors of the present invention have carried out extensivestudies to produce a high-strength target for forming a protective filmfor an optical recording medium without producing cracks even inhigh-power sputtering. As a result, the following results are obtained.

(a) As for a sputtering target for forming a protective film for anoptical recording medium produced by sintering a mixed powder including10 to 70% of zirconium oxide, and 50% or less (over 0%) of silicondioxide, and the remainder containing aluminum oxide and inevitableimpurities; a sputtering target for forming a protective film for anoptical recording medium produced by sintering a mixed powder including10 to 70% of hafnium oxide, and 50% or less (over 0%) of silicondioxide, and the remainder containing aluminum oxide and inevitableimpurities; or a sputtering target for forming a protective film for anoptical recording medium produced by sintering a mixed powder containing10 to 70% of zirconium oxide, 0.1 to 8.4% of yttrium oxide, and 50% orless (over 0%) of silicon dioxide, and the remainder containing analuminum oxide and inevitable impurities; a target having a structure inwhich a complex oxide phase of Al₆Si₂O₁₃ is formed in a target base hasfurther improved density and strength. Thus, cracks do not occur in thetarget during high-power sputtering.

(b) As for a sputtering target for forming a protective film for anoptical recording medium produced by sintering a mixed powder including10 to 70% of zirconium oxide, and 50% or less (over 0%) of silicondioxide, and the remainder containing lanthanum oxide and inevitableimpurities; a sputtering target for forming a protective film for anoptical recording medium produced by sintering a mixed powder including10 to 70% of hafnium oxide, and 50% or less (over 0%) of a silicondioxide, and the remainder containing a lanthanum oxide and inevitableimpurities; or a sputtering target for forming a protective film for anoptical recording medium produced by sintering a mixed powder including10 to 70% of zirconium oxide, 0.1 to 8.4% of yttrium oxide, and 50% orless (over 0%) of silicon dioxide, and the remainder containing alanthanum oxide and inevitable impurities; a target having a structurein which a complex oxide phase of La₂SiO₅ is formed in a target base hasfurther improved density and strength. Thus, cracks do not occur in thetarget during high-power sputtering.

(c) As for a sputtering target for forming a protective film for anoptical recording medium produced by sintering a mixed powder including10 to 70% of zirconium oxide, and 50% or less (over 0%) of silicondioxide, and the remainder containing indium oxide and inevitableimpurities; a sputtering target for forming a protective film for anoptical recording medium produced by sintering a mixed powder including10 to 70% of hafnium oxide, and 50% or less (over 0%) of silicondioxide, and the remainder containing an indium oxide and inevitableimpurities; or a sputtering target for forming a protective film for anoptical recording medium produced by sintering a mixed powder including10 to 70% of zirconium oxide, 0.1 to 8.4% of yttrium oxide, and 50% orless (over 0%) of silicon dioxide, and the remainder containing anindium oxide and inevitable impurities; a target having a structure inwhich a complex oxide phase of In₂Si₂O₇ is formed in a target base hasfurther improved density and strength. Thus, cracks do not occur in thetarget during high-power sputtering. A target having a structure inwhich a complex oxide phase of In₂Si₂O₇ is formed in a target base givesmore remarkably improved density and strength as compared to a targethaving no complex oxide phase of In₂Si₂O₇.

The present invention has been made on the basis of these study results.

(1) According to a first embodiment of the invention, there is provideda high-strength sputtering target for forming a protective film for anoptical recording medium, obtained by sintering a mixed powderincluding, in mol %, 10 to 70% of zirconium oxide, and 50% or less (over0%) of silicon dioxide, and the remainder containing an aluminum oxideand inevitable impurities; the target has a structure in which a complexoxide phase of Al₆Si₂O₁₃ is formed in a target base. More preferably,the content of the zirconium oxide is in the range of 20 to 50 mol %,and the content of the silicon dioxide is in the range of 10 to 30 mol%.

(2) According to another embodiment of the invention, there is provideda high-strength sputtering target for forming a protective film for anoptical recording medium, obtained by sintering a mixed powderincluding, in mol %, 10 to 70% of hafnium oxide, and 50% or less (over0%) of silicon dioxide, and the remainder containing aluminum oxide andinevitable impurities; the target has a structure in which a complexoxide phase of Al₆Si₂O₁₃ is formed in a target base. More preferably,the content of the hafnium oxide is in the range of 20 to 50 mol %, andthe content of the silicon oxide is in the range of 10 to 30 mol %.

(3) According to another embodiment of the present invention, there isprovided a high-strength sputtering target for forming a protective filmfor an optical recording medium, obtained by sintering a mixed powderincluding, in mol %, 10 to 70% of zirconium oxide, 0.1 to 8.4% ofyttrium oxide, and 50% or less (over 0%) of a silicon dioxide, and theremainder containing an aluminum oxide and inevitable impurities; thetarget has a structure in which a complex oxide phase of Al₆Si₂O₁₃ isformed in a target base. More preferably, the content of the zirconiumoxide is in the range of 20 to 50 mol %, and the content of the siliconoxide is in the range of 10 to 30 mol %.

(4) According to another embodiment of the present invention, there isprovided a high-strength sputtering target for forming a protective filmfor an optical recording medium, obtained by sintering a mixed powderincluding, in mol %, 10 to 70% of zirconium oxide, and 50% or less (over0%) of silicon dioxide, and the remainder containing lanthanum oxide andinevitable impurities; the target has a structure in which a complexoxide phase of La₂SiO₅ is formed in a target base. More preferably, thecontent of the zirconium oxide is in the range of 20 to 50 mol %, andthe content of the silicon oxide is in the range of 10 to 30 mol %.

(5) According to another embodiment of the present invention, there isprovided a high-strength sputtering target for forming a protective filmfor an optical recording medium, obtained by sintering a mixed powderincluding, in mol %, 10 to 70% of hafnium oxide, and 50% or less (over0%) of silicon dioxide, and the remainder containing lanthanum oxide andinevitable impurities; the target has a structure in which a complexoxide phase of La₂SiO₅ is formed in a target base. More preferably, thecontent of the hafnium oxide is in the range of 20 to 50 mol %, and thecontent of the silicon oxide is in the range of 10 to 30 mol %.

(6) According to another embodiment of the present invention, there isprovided a high-strength sputtering target for forming a protective filmfor an optical recording medium, obtained by sintering a mixed powderincluding, in mol %, 10 to 70% of zirconium oxide, 0.1 to 8.4% ofyttrium oxide, and 50% or less (over 0%) of silicon dioxide, and theremainder containing lanthanum oxide and inevitable impurities, thetarget has a structure in which a complex oxide phase of La₂SiO₅ isformed in a target base. More preferably, the content of the zirconiumoxide is in the range of 20 to 50 mol %, and the content of the siliconoxide is in the range of 10 to 30 mol %.

(7) According to another embodiment of the present invention, there isprovided a high-strength sputtering target for forming a protective filmfor an optical recording medium, obtained by sintering a mixed powderincluding, in mol %, 10 to 70% of zirconium oxide, and 50% or less (over0%) of silicon dioxide, and the remainder containing indium oxide andinevitable impurities; the target has a structure in which a complexoxide phase of In₂Si₂O₇ is formed in a target base. More preferably, thecontent of the zirconium oxide is in the range of 20 to 50 mol %, andthe content of the silicon oxide is in the range of 10 to 30 mol %.

(8) According to another embodiment of the present invention, there isprovided a high-strength sputtering target for forming a protective filmfor an optical recording medium, obtained by sintering a mixed powderincluding, in mol %, 10 to 70% of hafnium oxide, and 50% or less (over0%) of silicon dioxide, and the remainder containing indium oxide andinevitable impurities; the target has a structure in which a complexoxide phase of In₂Si₂O₇ is formed in a target base. More preferably, thecontent of the hafnium oxide is in the range of 20 to 50 mol %, and thecontent of the silicon oxide is in the range of 10 to 30 mol %.

(9) According to another embodiment of the present invention, there isprovided a high-strength sputtering target for forming a protective filmfor an optical recording medium, obtained by sintering a mixed powderincluding, in mol %, 10 to 70% of zirconium oxide, 0.1 to 8.4% ofyttrium oxide, and 50% or less (over 0%) of silicon dioxide, and theremainder containing indium oxide and inevitable impurities; the targethas a structure in which a complex oxide phase of In₂Si₂O₇ is formed ina target base. More preferably, the content of the zirconium oxide is inthe range of 20 to 50 mol %, and the content of the silicon oxide is inthe range of 10 to 30 mol %.

For producing a high-strength sputtering target for forming a protectivefilm for an optical recording medium according to the present invention,zirconium oxide powder, yttira stabilized zirconia powder, hafnium oxidepowder, amorphous silicon dioxide powder, aluminum oxide powder,lanthanum oxide powder, and indium oxide powder are employed as rawpowders. These raw powders are combined and mixed to give compositionsmentioned in (1) to (9), thereby preparing mixed powders. The mixedpowders are press molded, after which the molded bodies are activelysintered at 1300° C. or higher, which is higher than the usual sinteringtemperature, in an oxygen atmosphere, thereby producing targets.

When producing a high-strength sputtering target for forming aprotective film for an optical recording medium according to the presentinvention, it is crucial to use an amorphous silicon dioxide powder asthe raw powder, to adopt an oxygen atmosphere, and to conduct baking ata temperature of 1300° C. or higher. If a crystalline silicon dioxidepower is used, warpage occurs in the produced target, which is notpreferable as the strength decreases. Furthermore, zirconium oxidepowder to be used as the raw powder may be a stabilized orpartially-stabilized zirconium oxide powder. As such the stabilized orpartially-stabilized zirconium oxide powder, for example, there is azirconium oxide powder containing 1 to 12 mol % of Y₂O₃.

A target for forming a protective film of an optical recording mediumaccording to the invention can be made larger since the strength of theprotective film is further improved. Moreover, since cracks do not formin the target even under a high-power sputtering, a protective film foran optical recording medium can be formed more efficiently.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinbelow, the target for forming a protective film for an opticalrecording medium according to the present invention will be described inmore detail with reference to Examples.

The following powders were prepared as the raw powders: ZrO₂ powderhaving an average particle diameter of 0.2 μm and a purity of 99.99% orhigher, HfO₂ powder having an average particle diameter of 0.2 μm and apurity of 99.99% or higher, SiO₂ powder having an average particlediameter of 0.2 μm and a purity of 99.99% or higher, SiO₂ powder havingan average particle diameter of 1 μm and a purity of 99.99% or higher,In₂O₃ powder having an average particle diameter of 0.5 μm and a purityof 99.99% or higher, Al₂O₃ powder having an average particle diameter of0.5 μm and a purity of 99.99% or higher, and La₂O₃ powder having anaverage particle diameter of 0.5 μm and a purity of 99.99% or higher. Inaddition, a stabilized ZrO₂ powder containing 3 mol % of Y₂O₃ was alsoprepared.

Example 1

The ZrO₂ powder, amorphous SiO₂ powder, crystalline SiO₂ powder, andAl₂O₃ powder were weighed to give the composition shown in Table 1 anduniformly mixed by a Henschel mixer. Subsequently, the mixed powder waspress-molded, after which the obtained molded body was baked under theconditions given in Table 1, thereby producing an inventive target 1 anda conventional target 1, both of which had a diameter of 200 mm and athickness of 6 mm and included 30% of ZrO₂, and 20% of SiO₂, and theremainders containing Al₂O₃. The cross sections of the target 1 of thepresent invention and the conventional target 1 were polished andobserved through X-ray diffraction and an EPMA to determine whether ornot a complex oxide phase of Al₆Si₂O₁₃ was formed in the bases of thetargets. The results of which are given in Table 1. Furthermore, thedensity and flexural strength of the target 1 of the present inventionand the conventional target 1 were measured. The results are shown inTable 1.

Then, the produced target 1 of the present invention and the producedconventional target 1 were mounted in a direct current magnetronsputtering system, in a state of being soldered with a water-cooledbacking plate made of oxygen-free copper. First, the inside of thesystem was evacuated to be 1×10⁻⁶ Torr or less using a vacuum airexhauster. Then, an Ar gas was introduced into the system so as to givea pressure of sputtering gas of 1.5×10⁻³ Torr. A polycarbonate substratewith a thickness of 0.6 mm was disposed at an interval of 70 mm, i.e.,the interval of the targets. In this state, a direct current power,i.e., a sputtering power of 9 kW which was higher than the norm, wasapplied, and protective films for an optical recording medium, having athickness of 50 nm, were formed on a surface of the polycarbonatesubstrate, using the target 1 of the present invention and theconventional target 1, respectively. Here, observation to determinewhether or not cracks are formed in the targets was made. The results ofwhich are shown in Table 1.

TABLE 1 Existence or Properties of Target Nonexistence Existence orConditions of Baking of Complex Nonexistence Composition of Raw Powder(mol %) Tem- Keeping Oxide of Flexural of Cracks Amorphous Crystallineperature Time Al₆Si₂O₁₃ in Density Strength during Target ZrO₂ SiO₂ SiO₂Al₂O₃ Atmosphere (° C.) (h) Target Base (%) (MPa) Sputtering Present 130 20 — remainder oxygen 1400 7 Existent 96 275 Nonexistent InventionConventional 1 30 — 20 remainder air 1200 7 Nonexistent 85 150 ExistentInvention

The results given in Table 1 show that the target 1 of the presentinvention in which the complex oxide phase of Al₆Si₂O₁₃ was formed inthe base has a higher density and strength and does not give cracks uponsputtering as compared to the conventional target 1 in which the complexoxide phase of Al₆Si₂O₁₃ was not formed in the base, even if both hadthe same composition.

Example 2

The HfO₂ powder, amorphous SiO₂ powder, crystalline SiO₂ powder, andAl₂O₃ powder were weighed to give the composition shown in Table 2 anduniformly mixed by a Henschel mixer. Subsequently, the mixed powder waspress-molded, after which the obtained molded body was baked under theconditions given in Table 2, thereby producing an inventive target 2 anda conventional target 2, both of which had a diameter of 200 mm and athickness of 6 mm and included 30% of HfO₂, and 20% of SiO₂, and theremainders containing Al₂O₃. The cross sections of the target 2 of thepresent invention and the conventional target 2 were polished andobserved through X-ray diffraction and an electron probe micro analyzer(EPMA) to determine whether or not a complex oxide phase of Al₆Si₂O₁₃was formed in the bases of the targets, the results of which are givenin Table 2. Furthermore, the density and flexural strength of the target2 of the present invention and the conventional target 2 were measured.The results are shown in Table 2.

Then, the produced target 2 of the present invention and the producedconventional target 2 were mounted in a direct current magnetronsputtering system, in a state of being soldered with a water-cooledbacking plate made of oxygen-free copper. First, the inside of thesystem was evacuated to be 1×10⁻⁶ Torr or less using a vacuum airexhauster. Then, an Ar gas was introduced into the system so as to givea pressure of sputtering gas of 1.5×10⁻³ Torr. A polycarbonate substratewith a thickness of 0.6 mm was disposed at an interval of 70 mm, i.e.,the interval of the targets. In this state, direct current power, i.e.,a sputtering power of 7 kW which was higher than norm, was applied, andprotective films for an optical recording medium, having a thickness of50 nm, were formed on a surface of the polycarbonate substrate, usingthe target 2 of the invention and the conventional target 2,respectively. Here, observation to determine whether or not cracks areformed in the targets was made. The results of which are shown in Table2.

TABLE 2 Existence or Properties of Target Nonexistence Existence orConditions of Baking of Complex Nonexistence Composition of Raw Powder(mol %) Tem- Keeping Oxide of Flexural of Cracks Amorphous Crystallineperature Time Al₆Si₂O₁₃ in Density Strength during Target HfO₂ SiO₂ SiO₂Al₂O₃ Atmosphere (° C.) (h) Target Base (%) (MPa) Sputtering Present 230 20 — Remainder oxygen 1400 7 Existent 97 220 Nonexistent InventionConventional 2 30 — 20 Remainder air 1200 7 Nonexistent 85 145 ExistentInvention

The results given in Table 2 show that the target 2 of the presentinvention in which the complex oxide phase of Al₆Si₂O₁₃ was formed inthe base has a higher density and strength and does not give cracks uponsputtering as compared to the conventional target 2 in which the complexoxide phase of Al₆Si₂O₁₃ was not formed in the base, even if both hadthe same composition.

Example 3

The stabilizer ZrO₂ powder containing 3 mol % of Y₂O₃, amorphous SiO₂powder, crystalline SiO₂ powder, and Al₂O₃ powder were weighed to givethe composition given in Table 3 and uniformly mixed by a Henschelmixer. Subsequently, the mixed powder was press-molded, after which theobtained molded body was baked under the conditions given in Table 3,thereby producing a target 3 of the present invention and a conventionaltarget 3, both of which had a diameter of 200 mm and a thickness of 6 mmand included 30% of ZrO₂, and 0.9% of Y₂O₃, 20% of SiO₂, and theremainders containing Al₂O₃. The cross sections of the target 3 of thepresent invention and the conventional target 3 were polished andobserved through X-ray diffraction and an electron probe micro analyzer(EPMA) to determine whether or not a complex oxide phase of Al₆Si₂O₁₃was formed in the bases of the targets, the results of which are givenin Table 3. Furthermore, the density and flexural strength of the target3 of the present invention and the conventional target 3 were measured.The results are shown in Table 3.

Then, the produced target 3 of the present invention and the producedconventional target 3 were mounted in a direct current magnetronsputtering system, in a state of being soldered with a water-cooledbacking plate made of oxygen-free copper. First, the inside of thesystem was evacuated to be 1×10⁻⁶ Torr or less using a vacuum airexhauster. Then, an Ar gas was introduced into the system so as to givea pressure of sputtering gas of 1.5×10⁻³ Torr. A polycarbonate substratewith a thickness of 0.6 mm was disposed at an interval of 70 mm, i.e.,the interval of the targets. In this state, a direct current power,i.e., a sputtering power of 9 kW which was higher than the norm, wasapplied, and protective films for an optical recording medium, having athickness of 50 nm, were formed on the polycarbonate substrate, usingthe target 3 of the present invention and the conventional target 3,respectively. Here, observation to determine whether or not cracks areformed in the targets was made. The results of which are shown in Table3.

TABLE 3 Composition of Raw Powder (mol %) Existence or Properties ofTarget Stabilizer Conditions of Baking Nonexistence Existence or ZrO₂Tem- of Complex Nonexistence Containing pera- Keeping Oxide of Flexuralof Cracks 3 mol % of Amorphous Crystalline Atmos- ture Time Al₆Si₂O₁₃ inDensity Strength during Target Y₂O₃ SiO₂ SiO₂ Al₂O₃ phere (° C.) (h)Target Base (%) (MPa) Sputtering Present 3 30 20 — Remainder oxygen 14007 Existent 99 280 Nonexistent Invention Conventional 3 30 — 20 Remainderair 1200 7 Nonexistent 92 200 Existent Invention

The results given in Table 3 show that the target 3 of the presentinvention in which the complex oxide phase of Al₆Si₂O₁₃ was formed inthe base has a higher density and strength and does not give uponsputtering as compared to the conventional target 3 in which the complexoxide phase of Al₆Si₂O₁₃ was not formed in the base, even if both hadthe same composition.

Example 4

The ZrO₂ powder, amorphous SiO₂ powder, crystalline SiO₂ powder, andLa₂O₃ powder were weighed to give the composition given in Table 4 anduniformly mixed by a Henschel mixer. Subsequently, the mixed powder waspress-molded, after which the obtained molded body was baked under theconditions given in Table 4, thereby producing a target 4 of the presentinvention and a conventional target 4, both of which had a diameter of200 mm and a thickness of 6 mm and included 30% of ZrO₂, and 20% ofSiO₂, and remainders containing La₂O₃. The cross sections of the target4 of the present invention and the conventional target 4 were polishedand observed through X-ray diffraction and an electron probe microanalyzer (EPMA) to determine whether or not a complex oxide phase ofLa₂SiO₅ was formed in the bases of the targets. The results of which aregiven in Table 4. Furthermore, the density and flexural strength of thetarget 4 of the present invention and the conventional target 4 weremeasured. The results are shown in Table 4.

Then, the produced target 4 of the present invention and the producedconventional target 4 were mounted in a direct current magnetronsputtering system, in a state of being soldered with a water-cooledbacking plate made of oxygen-free copper. First, the inside of thesystem was evacuated to be 1×10⁻⁶ Torr or less using a vacuum airexhauster. Then, an Ar gas was introduced into the system so as to givea pressure of sputtering gas of 1.5×10⁻³ Torr. A polycarbonate substratewith a thickness of 0.6 mm was disposed at an interval of 70 mm, i.e.,the interval of the targets. In this state, a direct current power,i.e., a sputtering power of 9 kW which was higher than the norm, wasapplied, and protective films for an optical recording medium, having athickness of 50 nm, were formed on a surface of the polycarbonatesubstrate, using the target 4 of the present invention and theconventional target 4, respectively. Here, observation to determinewhether or not cracks are formed in the targets was made. The results ofwhich are shown in Table 4.

TABLE 4 Existence or Properties of Target Conditions of BakingNonexistence Existence or Tem- of Complex Nonexistence Composition ofRaw Powder (mol %) pera- Oxide of Flexural of Cracks AmorphousCrystalline ture Keeping La₃SiO₅ in Density Strength during Target ZrO₂SiO₂ SiO₂ La₂O₃ Atmosphere (° C.) Time (h) Target Base (%) (MPa)Sputtering Present 4 30 20 — Remainder oxygen 1400 7 Existent 95 190Nonexistent Invention Conventional 4 30 — 20 Remainder air 1200 7Nonexistent 85 110 Existent Invention

The results given in Table 4 show that the target 4 of the presentinvention in which the complex oxide phase of La₂SiO₅ was formed in thebase has a higher density and strength and does not give cracks uponsputtering as compared to the conventional target 4 in which the complexoxide phase of La₂SiO₅ was not formed in the base, even if both had thesame composition.

Example 5

The HfO₂ powder, amorphous SiO₂ powder, crystalline SiO₂ powder, andLa₂O₃ powder were weighed to give the composition given in Table 5 anduniformly mixed by a Henschel mixer. Subsequently, the mixed powder waspress-molded, after which the obtained molded body was baked under theconditions given in Table 5, thereby producing a target 5 of the presentinvention and a conventional target 5, both of which had a diameter of200 mm and a thickness of 6 mm and included 30% of HfO₂, and 20% ofSiO₂, and the remainders containing La₂O₃. The cross sections of thetarget 5 of the present invention and the conventional target 5 werepolished and observed through X-ray diffraction and an electron probemicro analyzer (EPMA) to determine whether or not a complex oxide phaseof La₂SiO₅ was formed in the bases of the targets. The results of whichare given in Table 5. Furthermore, the density and flexural strength ofthe target 5 of the present invention and the conventional target 5 weremeasured. The results of which are shown in Table 5.

Then, the produced target 5 of the present invention and the producedconventional target 5 were mounted in a direct current magnetronsputtering system, in a state of being soldered with a water-cooledbacking plate made of oxygen-free copper. First, the inside of thesystem was evacuated to be 1×10⁻⁶ Torr or less using a vacuum airexhauster. Then, an Ar gas was introduced into the system so as to givea pressure of sputtering gas of 1.5×10⁻³ Torr. A polycarbonate substratewith a thickness of 0.6 mm was disposed at an interval of 70 mm, i.e.,the interval of the targets. In this state, a direct current power,i.e., a sputtering power of 7 kW which was higher than the norm, wasapplied, and protective films for an optical recording medium, having athickness of 50 nm, were formed on a surface of the polycarbonatesubstrate, using the target 5 of the present invention and theconventional target 5, respectively. Here, observation to determinewhether or not cracks are formed in the targets was made. The results ofwhich are shown in Table 5.

TABLE 5 Existence or Properties of Target Conditions of BakingNonexistence Existence or Tem- of Complex Nonexistence Composition ofRaw Powder (mol %) pera- Oxide of Flexural of Cracks AmorphousCrystalline ture Keeping La₃SiO₅ in Density Strength during Target HfO₂SiO₂ SiO₂ La₂O₃ Atmosphere (° C.) Time (h) Target Base (%) (MPa)Sputtering Present 5 30 20 — Remainder oxygen 1400 7 Existent 98 180Nonexistent Invention Conventional 5 30 — 20 Remainder air 1200 7Nonexistent 85 100 Existent Invention

The results given in Table 5 show that the target 5 of the presentinvention in which the complex oxide phase of La₂SiO₅ was formed in thebase has a higher density and strength and does not give cracks uponsputtering as compared to the conventional target 5 in which the complexoxide phase of La₂SiO₅ was not formed in the base, even if both had thesame composition.

Example 6

The stabilizer ZrO₂ powder containing 3 mol % of Y₂O₃, amorphous SiO₂powder, crystalline SiO₂ powder, and La₂O₃ powder were weighed to givethe composition shown in Table 6 and uniformly mixed by a Henschelmixer. Subsequently, the mixed powder was press-molded, after which theobtained molded body was baked under the condition given in Table 6,thereby producing a target 6 of the present invention and a conventionaltarget 6, both of which had a diameter of 200 mm and a thickness of 6 mmand included 30% of ZrO₂, and 0.9% of Y₂O₃, 20% of SiO₂ and theremainders containing La₂O₃. The cross sections of the target 6 of thepresent invention and the conventional target 6 were polished andobserved through X-ray diffraction and an electron probe micro analyzer(EPMA) to determine whether or not a complex oxide phase of La₂SiO₅ wasformed in the bases of the targets. The results of which are given inTable 6. Furthermore, the density and flexural strength of the target 6of the present invention and the conventional target 6 were measured.The results are shown in Table 6.

Then, the produced target 6 of the present invention and the producedconventional target 6 were mounted in a direct current magnetronsputtering system, in a state of being soldered with a water-cooledbacking plate made of oxygen-free copper. First, the inside of thesystem was evacuated to be 1×10⁻⁶ Torr or less using a vacuum airexhauster. Then, an Ar gas was introduced into the system so as to givea pressure of sputtering gas of 1.5×10⁻³ Torr. A polycarbonate substratewith a thickness of 0.6 mm was disposed at an interval of 70 mm, i.e.,the interval of the targets. In this state, a direct current power,i.e., a sputtering power of 9 kW which was higher than the norm, wasapplied, and protective films for an optical recording medium, having athickness of 50 nm, were formed on a surface of the polycarbonatesubstrate, using the target 6 of the present invention and theconventional target 6, respectively. Here, observation to determinewhether or not cracks are formed in the targets was made. The results ofwhich are shown in Table 6.

TABLE 6 Existence or Composition of Raw Powder (mol %) NonexistenceProperties of Target Stabilizer Conditions of Baking of ComplexExistence or ZrO₂ Tem- Oxide of Nonexistence Containing pera- KeepingLa₃SiO₅ Flexural of 3 mol Amorphous Crystalline Atmos- ture Time inTarget Density Strength Cracks during Target % of Y₂O₃, SiO₂ SiO₂ La₂O₃phere (° C.) (h) Base (%) (MPa) Sputtering Present 6 30 20 — Remainderoxygen 1400 7 Existent 96 220 Nonexistent Invention Conventional 6 30 —20 Remainder air 1200 7 Nonexistent 89 145 Existent Invention

The results given in Table 6 show that the target 6 of the presentinvention in which the complex oxide phase of La₂SiO₅ was formed in thebase has a higher density and strength and does not give cracks uponsputtering as compared to the conventional target 6 in which the complexoxide phase of La₂SiO₅ was not formed in the base, even if both had thesame composition.

Example 7

The ZrO₂ powder, amorphous SiO₂ powder, crystalline SiO₂ powder, andIn₂O₃ powder were weighed to give the composition shown in Table 7 anduniformly mixed by a Henschel mixer. Subsequently, the mixed powder waspress-molded, after which the obtained molded body was baked under thecondition given in Table 7, thereby producing a target 7 of the presentinvention and a conventional target 7, both of which had a diameter of200 mm and a thickness of 6 mm and included 30% of ZrO₂, and 20% ofSiO₂, and the remainders containing In₂O₃. The cross sections of thetarget 7 of the present invention and the conventional target 7 werepolished and observed through X-ray diffraction and an electron probemicro analyzer (EPMA) to determine whether or not a complex oxide phaseof In₂Si₂O₇ was formed in the bases of the targets. The results of whichare given in Table 7. Furthermore, the density and flexural strength ofthe target 7 of the present invention and the conventional target 7 weremeasured. The results of which are shown in Table 7.

Then, the produced target 7 of the present invention and the producedconventional target 7 were mounted in a direct current magnetronsputtering system, in a state of being soldered with a water-cooledbacking plate made of oxygen-free copper. First, the inside of thesystem was evacuated to be 1×10⁻⁶ Torr or less using a vacuum airexhauster. Then, an Ar gas was introduced into the system so as to givea pressure of sputtering gas of 1.5×10⁻³ Torr. A polycarbonate substratewith a thickness of 0.6 mm was disposed at an interval of 70 mm, i.e.,the interval of the targets. In this state, a direct current power,i.e., a sputtering power of 9 kW which was higher than the norm, wasapplied, and protective films for an optical recording medium, having athickness of 50 nm, were formed on a surface of the polycarbonatesubstrate, using the target 7 of the present invention and theconventional target 7, respectively. Here, observation to determinewhether or not cracks are formed in the targets was made. The results ofwhich are shown in Table 7.

TABLE 7 Properties of Target Conditions of Baking Existence or Existenceor Tem- Nonexistence of Nonexistence Composition of Raw Powder (mol %)pera- Keeping Complex Oxide Flexural of Cracks Amorphous Crystallineture Time of In₂Si₂O₇ in Density Strength during Target ZrO₂ SiO₂ SiO₂In₂O₃ Atmosphere (° C.) (h) Target Base (%) (MPa) Sputtering Present 730 20 — Remainder oxygen 1400 7 Existent 99 255 Nonexistent InventionConventional 7 30 — 20 Remainder air 1200 7 Nonexistent 90 150 ExistentInvention

The results given in Table 7 show that the target 7 of the presentinvention in which the complex oxide phase of In₂Si₂O₇ was formed in thebase has a higher density and strength and does not give cracks uponsputtering as compared to the conventional target 7 in which the complexoxide phase of In₂Si₂O₇ was not formed in the base, even if both had thesame composition.

Example 8

The HfO₂ powder, amorphous SiO₂ powder, crystalline SiO₂ powder, andIn₂O₃ powder were weighed to give the composition shown in Table 8 anduniformly mixed by a Henschel mixer. Subsequently, the mixed powder waspress-molded, after which the obtained molded body was baked under theconditions given in Table 8, thereby producing a target 8 of the presentinvention and a conventional target 8, both of which had a diameter of200 mm and a thickness of 6 mm and included 30% of HfO₂, and 20% ofSiO₂, and the remainders containing In₂O₃. The cross sections of thetarget 8 of the present invention and the conventional target 8 werepolished and observed through X-ray diffraction and an electron probemicro analyzer (EPMA) to determine whether or not a complex oxide phaseof In₂Si₂O₇ was formed in the bases of the target. The results of whichare given in Table 8. Furthermore, the density and flexural strength ofthe target 8 of the present invention and the conventional target 8 weremeasured. The results are shown in Table 8.

Then, the produced target 8 of the present invention and the producedconventional target 8 were mounted in a direct current magnetronsputtering system, in a state of being soldered with a water-cooledbacking plate made of oxygen-free copper. First, the inside of thesystem was evacuated to be 1×10⁻⁶ Torr or less using a vacuum airexhauster. Then, an Ar gas was introduced into the system so as to givea pressure of sputtering gas of 1.5×10⁻³ Torr. A polycarbonate substratewith a thickness of 0.6 mm was disposed at an interval of 70 mm, i.e.,the interval of the targets. In this state, a direct current power,i.e., a sputtering power of 7 kW which was higher than the norm, wasapplied, and protective films for an optical recording medium, having athickness of 50 nm, were formed on a surface of the polycarbonatesubstrate, using the target 8 of the present invention and theconventional target 8, respectively. Here, observation to determinewhether or not cracks are formed in the targets was made. The results ofwhich are shown in Table 8.

TABLE 8 Existence or Properties of Target Conditions of BakingNonexistence Existence or Tem- of Complex Nonexistence Composition ofRaw Powder (mol %) pera- Oxide of Flexural of Cracks AmorphousCrystalline ture Keeping In₂Si₂O₇ in Density Strength during Target HfO₂SiO₂ SiO₂ In₂O₃ Atmosphere (° C.) Time (h) Target Base (%) (MPa)Sputtering Present 8 30 20 — Remainder oxygen 1400 7 Existent 98 200Nonexistent Invention Conventional 8 30 — 20 Remainder air 1200 7Nonexistent 90 150 Existent Invention

The results given in Table 8 show that the target 8 of the presentinvention in which the complex oxide phase of In₂Si₂O₇ was formed in thebase has a higher density and strength and does not give cracks uponsputtering as compared to the conventional target 8 in which the complexoxide phase of In₂Si₂O₇ was not formed in the base, even if both had thesame composition.

Example 9

The stabilizer ZrO₂ powder containing 3 mol % of Y₂O₃, amorphous SiO₂powder, crystalline SiO₂ powder, and In₂O₃ powder were weighed to givethe composition shown in Table 9 and uniformly mixed by a Henschelmixer. Subsequently, the mixed powder was press-molded, after which theobtained molded body was baked under the condition given in Table 9,thereby producing a target 9 of the present invention and a conventionaltarget 9, both of which had a diameter of 200 mm and a thickness of 6 mmand included 30% of ZrO₂, 0.9% of Y₂O₃, and 20% of SiO₂ and theremainders containing In₂O₃. The cross sections of the target 9 of thepresent invention and the conventional target 9 were polished andobserved through X-ray diffraction and an electron probe micro analyzer(EPMA) to determine whether or not a complex oxide phase of In₂Si₂O₇ wasformed in the bases of the targets. The results of which are given inTable 9. Furthermore, the density and flexural strength of the target 9of the present invention and the conventional target 9 were measured.The results are shown in Table 9.

Then, the produced target 9 of the present invention and the producedconventional target 9 were mounted in a direct current magnetronsputtering system, in a state of being soldered with a water-cooledbacking plate made of oxygen-free copper. First, the inside of thesystem was evacuated to be 1×10⁻⁶ Torr or less using a vacuum airexhauster. Then, an Ar gas was introduced into the system so as to givea pressure of sputtering gas of 1.5×10⁻³ Torr. A polycarbonate substratewith a thickness of 0.6 mm was disposed at an interval of 70 mm, i.e.,the interval of the targets. In this state, a direct current power,i.e., a sputtering power of 9 kW which was higher than the norm, wasapplied, and protective films for an optical recording medium, having athickness of 50 nm, were formed on a surface of the polycarbonatesubstrate, using the target 9 of the present invention and theconventional target 9, respectively. Here, observation to determinewhether or not cracks are formed in the targets was made. The results ofwhich are shown in Table 9.

TABLE 9 Existence or Composition of Raw Powder (mol %) NonexistenceProperties of Target Stabilizer Conditions of Baking of Existence orZrO₂ Tem- Complex Oxide Nonexistence Containing pera- Keeping ofIn₂Si₂O₇ Flexural of 3 mol Amorphous Crystalline Atmos- ture Time inTarget Density Strength Cracks upon Target % of Y₂O₃, SiO₂ SiO₂ In₂O₃phere (° C.) (h) Base (%) (MPa) Sputtering Present 9 30 20 — Remainderoxygen 1400 7 Existent 99 255 Nonexistent Invention Conventional 9 30 —20 Remainder air 1200 7 Nonexistent 90 150 Existent Invention

The results given in Table 9 show that the target 9 of the presentinvention in which the complex oxide phase of In₂Si₂O₇ was formed in thebase has a higher density and strength and does not give cracks uponsputtering as compared to the conventional target 9 in which the complexoxide phase of In₂Si₂O₇ was not formed in the base, even if both had thesame composition.

As described above, a target for forming a protective film for anoptical recording medium according to the present invention can beformed in a large size due to even more improved strength. Moreover, ascracks do not form in the target even under high-power sputtering, aprotective film for an optical recording medium can be formed moreefficiently. Accordingly, the present invention is substantially usefulfor industrial applications.

1. A high-strength sputtering target for forming a protective film foran optical recording medium, obtained by sintering a mixed powderconsisting of, in mol %, 10 to 70% of zirconium oxide, and 50% or lessand more than 0% of silicon dioxide including an amorphous silicondioxide, and the remainder containing indium oxide, wherein a complexoxide phase of In₂Si₂O₇ is formed in a base of the target.
 2. Thehigh-strength sputtering target according to claim 1, obtained bysintering a mixed powder consisting of, in mol %, 20 to 50% of thezirconium oxide, 10 to 30% of the silicon dioxide, and the remainder isthe indium oxide.
 3. The high-strength sputtering target according toclaim 1, the silicon dioxide is all amorphous silicon dioxide.
 4. Ahigh-strength sputtering target for forming a protective film for anoptical recording medium, obtained by sintering a mixed powderconsisting of, in mol %, 10 to 70% of zirconium oxide, 0.1 to 8.4% ofyttrium oxide, and 50% or less and more than 0% of silicon dioxideincluding an amorphous silicon dioxide, and the remainder containingindium oxide, wherein a complex oxide phase of In₂Si₂O₇ is formed in abase of the target.
 5. The high-strength sputtering target according toclaim 4, obtained by sintering a mixed powder consisting of, in mol %,20 to 50% of the zirconium oxide, 0.1 to 8.4% of the yttrium oxide, 10to 30% of the silicon dioxide, and the remainder is the indium oxide. 6.The high-strength sputtering target according to claim 4, the silicondioxide is all amorphous silicon dioxide.
 7. A method for producing ahigh-strength sputtering target with a complex oxide phase of In₂Si₂O₇formed in a base of the target, for a protective film for an opticalrecording medium comprising the steps of: press molding a mixed powderconsisting of, in mol %, 10 to 70% of zirconium oxide, and 50% or lessand more than 0% of silicon dioxide, and the remainder containing indiumoxide; and sintering said mixed powder in an oxygen atmosphere at 1300°C. or higher to form the complex oxide phase of In₂Si₂O₇ in the base ofthe target, wherein, the silicon dioxide in the mixed powder includes anamorphous silicon dioxide.
 8. The method for producing a high-strengthsputtering target according to claim 7, wherein the mixed powderconsists of, in mol %, 20 to 50% of the zirconium oxide, 10 to 30% ofthe silicon dioxide, and the remainder is the indium oxide.
 9. Themethod for producing a high-strength sputtering target according toclaim 7, the silicon dioxide is all amorphous silicon dioxide.
 10. Amethod for producing a high-strength sputtering target with a complexoxide phase of In₂Si₂O₇ formed in a base of the target, for a protectivefilm for an optical recording medium comprising the steps of: pressmolding a mixed powder consisting of, in mol %, 10 to 70% of zirconiumoxide, 0.1 to 8.4% of yttrium oxide, and 50% or less and more than 0% ofsilicon dioxide, and the remainder containing indium oxide; andsintering said mixed powder in an oxygen atmosphere at 1300° C. orhigher to form the complex oxide phase of In₂Si₇O₇ in the base of thetarget, wherein, the silicon dioxide in the mixed powder includes anamorphous silicon dioxide.
 11. The method for producing a high-strengthsputtering target according to claim 10, wherein the mixed powderconsists of, in mol %, 20 to 50% of the zirconium oxide, 0.1 to 8.4% ofyttrium oxide, 10 to 30% of the silicon dioxide, and the remainder isthe indium oxide.
 12. The method for producing a high-strengthsputtering target according to claim 10, the silicon dioxide is allamorphous silicon dioxide.